Evaluation of trap crops for the management of wireworms in spring wheat in Montana

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Wireworms, the larval stage of click beetles, have slender, shiny, hard bodies with three pairs of legs. They are polyphagous and have cryptic habitats. In recent years, increasing wireworm numbers and damage have become a major problem for growers in the Golden Triangle Region of Montana. The control of this pest is very difficult because after the removal of Lindane by US Environmental Protection Agency (USEPA) in 2009, the use of the second generation insecticides have not been able to provide effective control of wireworms. Thus, using insecticides to control wireworms has not been effective at high population levels. Also, little is known about the biology and feeding habit of wireworms. The goal of this study is to evaluate trap crops that can protect the spring wheat by attracting wireworms. First, field trials were conducted at two locations to investigate on the use of peas Pisum sativum L. (Fabaceae), lentils Lens culinaris L. (Fabaceae), canola/rapeseed Brassica napus L. (Brassicaceae), corn/maize Zea mays L. (Poaceae), durum Triticum durum Desf. (Poaceae) and barley Hordeum vulgare L. (Poaceae) as traps intercropped with spring wheat Triticum aestivum L. (Poaceae). The efficacy of trap cropping was determined by damage assessment in wheat plants along 1m transects and by counting wireworm populations on wheat and trap crop rows of a plot. Secondly, the effect of intercrop spacing on plant damage and the number of wireworms was determined for pea and lentil trap crops. To support field trials potted experiments were set up in the shade house to determine wireworm distributions in two-choice assays. Collectively the results from this study showed that pea and lentil trap crops resulted in significantly lower damage in wheat plants and they attracted more numbers of wireworms compared to other crops. Results from shade house trails supported observations from the field trials. An intercropping spacing of 0.5m between pea or lentil and the spring wheat crop produced highest density of spring wheat plants. The results from these experiments will add to the basic understanding of trap cropping for wireworms control.